Far field telemetry operations between an external device and an implantable medical device during recharge of the implantable medical device via a proximity coupling

ABSTRACT

Far field telemetry operations are conducted between an external device and an implantable medical device while power is being transferred to the implantable medical device for purposes of recharging a battery of the implantable medical device. The far field operations may include exchanging recharge information that has been collected by the implantable medical device which allows the external device to exercise control over the recharge process. The far field operations may include suspending far field telemetry communications for periods of time while power continues to be transferred where suspending far field telemetry communications may include powering down far field telemetry communication circuits of the implantable medical device for periods of time which may conserve energy. The far field operations may further include transferring programming instructions to the implantable medical device.

TECHNICAL FIELD

Embodiments relate to recharge sessions between an implantable medicaldevice to be recharged and an external device in control of the rechargeenergy. More particularly, embodiments relate to conducting far fieldtelemetry operations between the implantable medical device and theexternal device while recharge energy is being transferred.

BACKGROUND

Implantable medical devices including those that are positioned on theexterior of a body of a patient as well as those that are positionedsubcutaneously or deeper typically utilize an on-board battery thatallows the patient to be untethered to a power source. The patientmaintains mobility while the implantable medical device performs aparticular medical task by operating on power from the battery. Forinstance, the implantable medical device may provide stimulation therapyfor neurological or cardiac conditions, may provide drug delivery forvarious conditions such as pain management, and/or may providephysiological monitoring.

While the on-board battery may power the medical device for a relativelylong period of time, the on-board battery will eventually be depleted.Prior to rechargeable medical systems, the implantable medical devicewould be replaced once the battery became depleted. With rechargeablemedical systems, an external device provides recharge energy over aproximity coupling, which is typically inductive, to the implantablemedical device. This recharge energy restores the on-board battery to asatisfactory level for continued operation of the medical device.

During a recharge session, the external device in control of therecharge energy and the implantable medical device to be rechargedexchange telemetry communications related to the recharge process.Recharge information such as battery status, coupling efficiency and thelike may be transferred in this manner so that the external device canproperly control delivery of the recharge energy as well as instruct auser. Conventionally, the two devices exchange telemetry communicationsover a proximity coupling. However, this proximity coupling is alsobeing used to transfer the recharge energy, and in some cases rechargingmay stop while the telemetry communications are conducted over theproximity coupling. This increases the amount of time needed to completethe recharge session.

SUMMARY

Embodiments address issues such as these and others by providing farfield telemetry operations between the external device and theimplantable medical device while power continues to be transferred tothe implantable medical device to recharge the battery. The far fieldtelemetry operations include exchanging by far field telemetrycommunications recharge information collected by the implantable medicaldevice that is used by the external device. The far field telemetryoperations may include suspending far field telemetry communications forperiods during the recharge session to reduce the amount of energy beingexpended by the implantable medical device during the recharge session.The far field telemetry operations may include sending programminginstructions to the implantable medical device such as where theexternal device receives a programming request from a user during therecharge session.

Embodiments provide a method of recharging an implantable medicaldevice. The method involves establishing a far field telemetrycommunication session with the implantable medical device andtransferring power over a proximity coupling to the implantable medicaldevice during the far field telemetry communication session. The methodfurther involves receiving recharge information from the implantablemedical device via the far field telemetry communication session whiletransferring power to the implantable medical device, and afterreceiving the recharge information, suspending the far field telemetrycommunication session for a period of time while transferring power tothe implantable medical device.

Embodiments provide a medical system that includes an external devicehaving a far field telemetry communication circuit and a rechargecircuit. The external device transfers power through a recharge head ofthe recharge circuit while receiving recharge information through a farfield telemetry communication session via the far field telemetrycommunication circuit. The external device suspends the far fieldtelemetry communication session for a first period of time afterreceiving the recharge information by sending an instruction to closethe far field telemetry communication session to the implantable medicaldevice while continuing to transfer power. The medical system alsoincludes an implantable medical device having a far field telemetrycommunication circuit and a recharge circuit. The implantable medicaldevice receives transferred power via a proximity coupling of therecharge circuit to the recharge head of the external device whilesending recharge information through the far field telemetrycommunication session via the far field telemetry communication circuit.The implantable medical device closes the far field telemetrycommunication session upon receiving the instruction and listens for aninstruction to open the far field telemetry communication session aftereach occurrence of a second period that is no greater than the firstperiod while continuing to receive transferred power.

Embodiments provide an implantable medical device that includes amedical circuit that performs a medical task, a battery that providespower to the medical circuit, a recharge circuit that provides power tothe battery, a far field telemetry communication circuit, and aprocessor. The processor controls the recharge circuit and the far fieldtelemetry communication circuit, where the processor directs therecharge circuit to receive transferred power from a proximity couplingto a recharge head of an external device. The processor directs the farfield telemetry communication circuit to send recharge information via afar field telemetry communication session with the external device whilethe recharge circuit receives transferred power. The processor furtherdirects the far field telemetry communication circuit to power down inresponse to receiving a command to close the communication session withthe external device while the recharge circuit receives transferredpower. The processor periodically directs the far field telemetrycommunication circuit to power up and listen for a command to open thecommunication session while the recharge circuit receives transferredpower.

Embodiments provide a method of recharging an implantable medicaldevice. The method involves establishing a far field telemetrycommunication session with the implantable medical device andtransferring power over a proximity coupling to the implantable medicaldevice during the far field telemetry communication session. The methodfurther involves receiving recharge information from the implantablemedical device via the far field telemetry communication session whiletransferring power to the implantable medical device, and whiletransferring power, sending programming instructions to the implantablemedical device via the far field telemetry communication session.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a medical system according to variousembodiments.

FIG. 2 shows an example of components of an external device of themedical system.

FIG. 3 shows an example of components of an implantable medical deviceof the medical system.

FIGS. 4A-4C show examples of operations of the external device and theimplantable medical device of a medical system.

DETAILED DESCRIPTION

Embodiments provide for far field telemetry operations during rechargesessions between an external device and an implantable medical devicewhile the power used for recharge is being transferred to theimplantable medical device over a proximity coupling. Embodimentsprovide for the far field telemetry operations to be suspended forperiods of time while the power continues to be transferred. Embodimentsfurther provide for the far field telemetry operations to provideprogramming instructions to the implantable medical device while thepower continues to be transferred.

FIG. 1 shows an environment that includes an external device 102, suchas a clinician programmer-recharger or a patient programmer-rechargerthat is nearby a patient 108 who has an IMD 104. The IMD 104 may beimplanted within or mounted externally to the body 108 and may performone or more medical tasks such as cardiac or neurological stimulation,physiological sensing, drug infusion, and the like. The IMD 104 mayinclude components 106 such as stimulation or sensing leads or drugdelivery catheters that extend from the IMD 104 and terminate at thetarget area of the body 108.

The patient 108 ultimately wants the IMD 104 to be recharged so thatmedical therapy can continue. The external device 102 may providevarious functions including a recharge function whereby a rechargesession is established between the external device 102 and the IMD 104.During the recharge session, recharge energy is provided while a farfield telemetry communication session is also conducted to allow theexternal device 102 to receive feedback about charging status from theIMD 104 as well as for other purposes in some embodiments such as forprogramming the IMD 104 during the recharge session.

The external device 102 ultimately communicates with the IMD 104 duringa recharge session through a far field telemetry communication sessionutilizing far field signals 114 sent by the external device 102 and farfield signals 116 sent by the IMD 104. These far field signals 114, 116may be radio frequency (RF) signals such as those of the Medical ImplantCommunications Service (MICS) band, the Industrial, Scientific, andMedical (ISM) band, or the short range device (SRD) band. The far fieldtelemetry communication session may be used for additional purposesduring the recharge session as discussed below. Far field telemetrycommunications are those where a wave, i.e., via an E-field, ispropagated and that wave may be used to carry the communications asopposed to relying on an inductive coupling, i.e., via an H-field.

While the single IMD 104 is shown in FIG. 1, it will be appreciated thatthere may be other IMDs and/or other external devices nearby and inrange of the far field signals 114 of the external device 102. In someembodiments, the external device 102 may or may not be aware ofidentification information of the intended IMD 104 in advance such thatthe external device 102 cannot immediately discern far field telemetrycommunications of the intended IMD 104 relative to far field telemetrycommunications of other IMDs. However, physical proximity can beestablished to allow proximity communication 112 and/or recharge energytransfer 120 to occur between the external device 102 and the intendedIMD 104. Physical proximity refers to the intended IMD 104 beingpositioned closely to the external device 102 to the extent that anobserver such as a clinician can confirm that the intended IMD 104 isthe only IMD that can be responsive to proximity communications. Wherethe proximity communication is a signal from proximity telemetry, theproximity telemetry communications are those where the signal istypically an inductively coupled signal transfer, i.e., via an H-field.For proximity telemetry, the external device 102 must be within physicalproximity of the IMD (i.e., within the patient's “personal space”) forthe IMD to communicate with the external device. This is opposed to farfield communications wherein external device 102 may, but need not, bewithin physical proximity of the IMD to communicate with the IMD.

Therefore, a procedure is provided that utilizes this physical proximityat the initiation of the far field telemetry communication session andrelated recharge session to avoid the external device 102 conducting afar field telemetry communication session with an unintended nearby IMDwhile recharging the intended IMD 104. To allow the external device 102to select the intended IMD 104 for far field telemetry communicationduring a recharge session and avoid selecting an unintended nearby IMD,proximity communication signals 112 may be exchanged between a proximitycommunicator 110 and the IMD 104 during the establishment of the farfield telemetry communication session.

The proximity communicator 110 may be of various forms and may be aseparate component of the external device 102 or be integrated with theexternal device 102, or a combination of both. For instance, theproximity communicator 110 may be a near field telemetry head that istethered to the external device 102 by a communication path 118 such asa cable or wireless connection and that establishes an inductive linkwith the IMD 104. The proximity communicator 110 may utilize thetransfer of recharge energy as a proximity communication. As anotherexample, the proximity communicator 110 may be an audible tone generatorwhere the IMD 104 receives and recognizes different audible tones. Asanother example, the proximity communicator 110 may be a body thumpdevice, such as a chest thump device, where the IMD 104 detects thethump through an on-board accelerometer or other vibration detector. Asyet another example, the proximity communicator 110 may be a staticfield generating device such as an electromagnet or a permanent magnetbeing moved into and out of proximity with the IMD 104 by the clinician.

In some cases including the near field telemetry head, the audiblesignal generator, the body thump device, and the electromagnet, theproximity communicator 110 may be under control of the external device102 through a tethered or wireless connection between the telemetry head110 and the external device 102. In some cases including the clinicianproviding the body thump or moving the permanent magnet, the proximitycommunicator 110 is under direct control of the clinician who may befollowing commands being issued by the external device 102 to provide orremove the proximity communication.

The proximity communicator 110 may also integrate recharge circuitryincluding a recharge coil that inductively couples to a coil of the IMD104 to inductively transfer energy. Thus, a single tool may be placed inphysical proximity of the patient 108 in order to establish a form ofproximity communication and to delivery recharge energy. Where theconnection 118 is wired, recharge energy may be sourced from theexternal device 102. Where the connection 118 is wireless, the rechargeenergy may be sourced from an on-board power supply of the proximitycommunicator 110. As an alternative, the recharge device may be aseparate device from the proximity communicator 110 where both are heldin physical proximity to the patient 108 and linked to the externaldevice 102.

The proximity communication may range from being a simple present orabsent signal to a more complex signal carrying data. Furthermore, theproximity communication may be a unidirectional communication mode insome embodiments, particularly where the communication is simple. Thismay reduce the cost and complexity of a device, particularly the IMD104. One particular example of proximity communication may be thepresence or absence of recharge energy, and this recharge energy may bepulsed in accordance with a particular pattern that the IMD 104 maydiscern and which the IMD 104 may echo back to the external device 102.The proximity communication may be a bi-directional communication modein other embodiments, such as where one device may send data through aproximity communication while the other device may send anacknowledgement through a subsequent proximity communication. This mayimprove the efficiency of the proximity communication procedure.

FIG. 2 shows components of one example of the external device 102. Theexternal device 102 includes a processor 202, a memory 204, and astorage device 206. The external device 102 may also include localinput/output (I/O) ports 208 such as to provide local screen displaysand to receive user input via keyboard, mouse, and so forth. Theexternal device 102 also includes far field telemetry communicationcircuitry 210 used to establish the far field telemetry communicationsession with the IMD 104. The far field telemetry communicationcircuitry 210 may drive a signal propagation tool such as an RF antenna.The signal propagation tool may be included within the proximitycommunicator 110 so that the far field telemetry communication circuitry210 instructs the signal propagation tool over the connection 118 or thesignal propagation tool may be a separate external component or housedwithin the external device 102.

In addition to the far field telemetry communication circuitry 210, theexternal device 102 also includes proximity telemetry communicationcircuitry 212. The proximity telemetry communication circuitry 212 maybe of various forms to interact with the proximity communicator 110. Thelink between the proximity telemetry communication circuitry 212 and theproximity communicator 110 may be a wired or wireless connection, forexample using universal serial bus protocol, Bluetooth® protocol, orother such protocols, that provides data commands to circuitry withinthe proximity communicator 110 to produce the proximity communicationsignal. The proximity communicator 110 may then include a near fieldinductive driver circuit, a signal generator for producing audibletones, a motion signal generator for driving a body thump device, afield producing circuit for driving an electromagnet, and the like thatare responsive to the data commands. Alternatively for a wiredconnection, these circuits may be included in the proximity telemetrycommunication circuitry 212 to drive the proximity communicator 110directly.

The external device 102 may include additional communicationcapabilities that may be provided by far field telemetry communicationcircuitry 210 or by additional communication circuitry. For instance,the external device 102 may include Wi-Fi connectivity, public switchedtelephone network connectivity, and so forth to allow for remotecommunication, particularly where the external device 102 is a patientcontrolled device.

The external device 102 may include a recharge circuit 214 thatgenerates recharge waveforms to inductively transfer energy to the IMD104. The recharge circuit 214, for example, may include a coil that isdriven by a waveform generator that receives energy from a power supply.The recharge circuit 214 may utilize the coil that may be present withinthe proximity communicator 110 to deliver the recharge energy.

The memory 204 may be used to store information in use by the processor202. For instance, the memory 204 may store therapy parameters that areinput by a clinician or patient that are to be loaded into the IMD 104.The memory 204 may also store programming that is used by the processor202 to control the IMD selection procedure of the external device 102,to control the delivery of the recharge energy, and/or to controlperiodically suspending the far field telemetry communication sessionwhile the transfer of power continues. The memory 204 may be of varioustypes, such as volatile, non-volatile, or a combination of the two.

The storage device 206 may be used to store information for a long termand may be of various types such as non-volatile so that the informationis retained when the external device 102 is powered off. The storagedevice 206 may also store programming for the processor 202 that isimplemented to control the IMD selection procedure, the delivery ofrecharge energy, and the periodic suspension of the far field telemetrycommunication session while the power continues to be transferred.Examples of the storage device 206 include electronic, magnetic, andoptical drives including fixed and removable types such as securedigital cards and the like. The storage device 206 and the memory 204are both examples of computer readable media that may store informationin the form of computer programming, data structures, and the like.

The processor 202 performs logical operations to provide a sequence offar field and proximity communications, to control delivery of rechargeenergy, to control the far field telemetry communications and periodicsuspension, and to make related decisions such as those of FIGS. 4A-4Cto allow far field telemetry communication sessions with the IMD 104 tobe established in conjunction with a recharge session. The processor 202may be of various forms. For instance, the processor 202 may be ageneral-purpose programmable processor that executes software that isstored on the storage device 206 or elsewhere. Other examples include adedicated purpose hardware circuit or hard-wired digital logic. Theprocessor 202 may be multiple separate components or processors,dedicated hardware/state machine, and the like. The processor 202 maycommunicate with the various other components through one or more databuses.

FIG. 3 shows components of one example of the IMD 104 to be recharged.The IMD 104 includes a processor 302 and a memory 304. The IMD 104 alsoincludes medical circuitry 306 that performs a medical task such asstimulation, drug delivery, monitoring, and the like. The IMD 104 alsoincludes far field telemetry communication circuitry 308 used toestablish the far field telemetry communication session with theexternal device 102 independently of or in conjunction with a rechargesession. The far field telemetry communication circuitry 308 may drive asignal propagation tool such as an integral RF antenna.

In addition to the far field telemetry communication circuitry 308, theIMD 104 also includes proximity communication circuitry 310. Theproximity telemetry communication circuitry 310 may be of various formswhere for a given system, the type of proximity telemetry communicationcircuitry 310 matches the type of proximity communicator 110 that theexternal device 102 includes. Accordingly, the proximity telemetrycommunication circuitry 310 may be a near field inductive receiver, amicrophone for receiving audible tones, an accelerometer or othervibration detection device, a field operable switch such as a magneticreed switch, and the like.

The IMD 104 also includes a rechargeable battery 314 and a rechargecircuit 312 coupled to the battery 314. The recharge circuit 312 mayinclude a coil that inductively couples to the coil of the rechargecircuit 214 of the external device 102. The recharge circuit 312 mayutilize a dedicated coil or may utilize a coil that is also used by theproximity telemetry communication circuit 310. The recharge circuit 312may include rectification, filtering, voltage/current limiting, and thelike so as to provide an appropriate form of recharge power to thebattery 314.

The memory 304 may be used to store information in use by the processor302 such as programming and data values. The memory 304 may storeadditional information including therapy parameters that are used tocontrol the medical circuitry 306 as well as recharge parameters thatare used to control the recharge circuitry 312. The memory 304 may be ofvarious types such as volatile, non-volatile, or a combination of thetwo. The memory 304 is also an example of computer readable media thatmay store information in the form of computer programming, datastructures, and the like.

The processor 302 performs logical operations to provide a sequence offar field and proximity communications, to control delivery of rechargeenergy, to cooperate with the periodic suspension of the far fieldtelemetry communication session while the power continues to betransferred, and to make related decisions such as those of FIGS. 4A-4Cto allow far field telemetry communication sessions with the externaldevice 102 to be established independently of and in conjunction with arecharge session. The processor 302 may be of various forms like thosediscussed above for the processor 202 of the external device 102 and asdiscussed above may be multiple separate components or processors,dedicated hardware/state machine, and the like. The processor 302 maycommunicate with the various other components through one or more databuses.

FIG. 4A describes proximity based communications being used tofacilitate far field recharge sessions in conjunction with recharge orstatus sessions. While this example shows proximity communications beingdirected from an external device 102 to an IMD 104, it will beappreciated that in some cases the roles may be reversed and thedirection of the proximity communications may be reversed whereby theIMD 104 may send proximity communications rather than or in addition tothe external device 102 doing so.

FIG. 4A shows a first example of a procedure to establish a far fieldtelemetry communication session where a unique value and/or key areshared via a proximity communication. The proximity communication may beof a type that can carry data or may be a presence, absence, or patternof recharge energy. Furthermore, the proximity communication may bebi-directional so that an acknowledgement may be returned as aconfirmation of receipt of the data so that a successful initial datatransfer via the proximity communication can be completed as aprerequisite to attempting subsequent steps.

Initially, the external device 102 may store an identifier of a programbonded IMD and may also store a programming key for that bonded IMD asindicated at state 401. For security, some embodiments may preclude farfield telemetry communication between external devices 102 and IMDs 104unless the two are bonded, and utilizing the proximity communication isan example of bonding the two including sharing identifiers and/orprogramming keys. The identifier and programming key allows the externaldevice 102 to conduct a far field programming session without requiringa proximity communication to occur between the external device and theIMD where the two have already been bonded and where a programmingsession is being conducted. Thus for any given far field session, theprogramming key and identifier may have previously been exchanged byvirtue of a proximity based process.

In FIG. 4A, a recharge session is desired between the first externaldevice 102 and the first IMD 104 to be recharged. In this particularexample, because the user has selected to conduct a recharge session viathe external device, the bond that the external device 102 may have, ifany, is not applicable to initiating a far field telemetry communicationsession in conjunction with a recharge session. Exchanging a rechargekey to be used for far field telemetry communications during rechargevia the proximity communications and allowing the key to expire at theconclusion of the recharge session creates a temporary bond between theexternal device 102 and the IMD 104 to be recharged for purposes ofconducting far field telemetry communications during a recharge sessionwith an IMD 104 to be recharged. This may be useful, for instance, wherean external device of a clinician that has not been bonded to the IMD104 is being used to conduct the recharge session. In some embodiments,even where an external device 102 of the patient having the IMD 104 isbonded to the IMD 104 being recharged, a temporary bond via a rechargekey may be created. In other embodiments where the external device 102of the patient having the IMD 104 is bonded to the IMD 104, the rechargesession and related far field telemetry communication session may beginby utilizing the previously exchanged program key rather than exchanginga temporary recharge key.

The recharge session may be initiated in various ways according tovarious embodiments. For instance, the external device 102 may present amenu option to a user for beginning a recharge session. As anotherexample, the external device 102 may prompt the user as to whether tobegin recharge in response to some event, such as the user plugging in arecharge tool such as the proximity communicator 110 into the externaldevice. As yet another example, the external device 102 may begin therecharge session automatically in response to some event, such as theuser plugging in a recharge tool such as the proximity communicator 110in to the external device.

Initially, for embodiments where a bond does not exist or where a bondis not used for far field telemetry communications during a rechargesession, the external device 102 may send a proximity communication 402that includes a value that is unique to the external device 102 to theIMD 104. For example, the unique value may be a device serial number,hardware identification number, randomly generated number, a securitykey value, a combination, or other such values that may be unique to theexternal device 102. As another example, the proximity communication 402may be recharge energy that may be constant, pulsed, or otherwisemanipulated so as to be unique. Because this information is transferredthrough the proximity communication 402, no other nearby IMD willreceive this information or pattern of recharge energy. The externaldevice 102 also sends a far field discovery communication 404 shortlybefore, during, or shortly after sending the proximity communication402. The IMD 104 as well as other nearby IMDs may receive and respond tothis far field discovery communication 404.

In one example, the IMD 104 may respond only to a discovery request thatis within a certain time of receiving the proximity communication 402,such as a simultaneous occurrence of the proximity communication 402 andthe discovery communication 404 or within a predefined delay from one tothe next. In this example, the IMD 104 and potentially other nearby IMDsas well are configured to respond by sending the unique value that eachhas received via a proximity communication and also by sending a valuethat is unique to the IMD. For example, this value may be a deviceserial number, hardware identification number, randomly generatednumber, a security key value, a combination, or other such values thatmay be unique to the IMD 104.

Only the far field response communication 406 from the IMD 104 ofinterest will have the unique value that corresponds to the externaldevice 102. Other IMDs would either have no unique value of an externaldevice to send or would send the unique value of a different externaldevice. Furthermore, in some examples, only those IMDs that receive thediscovery communication 404 within a specified time relative to aproximity communication, such as the proximity communication 402received by the intended IMD 104, bother to respond with a far fieldresponse communication such as the far field response communication 406from the intended IMD 104.

For each far field response communication, the external device 102attempts to verify the shared unique value by determining whether theunique value being received matches the unique value that was previouslysent over the proximity communication 402 at a query operation 408. If aparticular response does not include a matching value, then thatparticular response is ignored at operation 410.

For embodiments using processes such as those of FIG. 4A where discoveryvia far field telemetry communications is attempted, the external device102 and IMDs may be configured to apply collision avoidance and backoffalgorithms. These algorithms allow devices to re-attempt to send and/orreceive expected far field telemetry communications where two devicesmay attempt to send a far field telemetry communication at the same timesuch that neither transmission is received and acknowledged. Are-attempt to send the far field telemetry communication occurs by eachof the sending devices but at different times on the second attemptsbecause the backoff algorithm of each sending device randomly choosesthe time for the re-attempt. This reduces the likelihood of collisionsoccurring multiple times. Thus, the external device 102 eventuallyreceives a discovery response that has not collided with another.Furthermore, the external device 102 eventually receives a discoveryresponse from the IMD 104 for which proximity communication 402 has beenestablished.

For the response 406 which does have the matching unique value from theproximity communication 402, the external device 102 then associates thevalue that is unique to the IMD 104 and that is included in the farfield response communication 406 to the far field telemetrycommunication session being established at an association operation 412.The external device 102 may also then execute the appropriate rechargeprogram automatically based on the value that is unique to the IMD 104where the external device 102 stores associations of such values torecharge applications.

The external device 102 then begins the far field telemetrycommunication session 414 and the related recharge session 416 with theIMD 104. The external device 102 may communicate during the far fieldsession 414 by using the unique value of the external device 102 ofwhich the IMD 104 is aware to identify the sender of transmissionsand/or using the unique value of the IMD 104 to identify the intendedrecipient of transmissions. Likewise, the IMD may communicate during thefar field session 414 by using the unique value of the IMD 104 of whichthe external device 102 is aware to identify the sender of transmissionsand/or using the unique value of the external device 102 to identify theintended recipient of transmissions.

The far field session 414 may be made secure by encrypting theinformation with an encryption key, such as the recharge key when atemporary bond has been created or the program key where a permanentbond has been previously created and is now being used. In the case of atemporary bond for the recharge session, the recharge key may have beengenerated for the session by the external device 102 and included in theproximity communication 402 so that the IMD 104 already has the key.Alternatively, the key may be exchanged in another manner and/or atanother time in the sequence such as by using a low power radiofrequency communication to minimize the range and thereby provide alevel of security for the transfer of the recharge key to the IMD 104.Furthermore, the IMD 104 may provide the recharge key for the secure farfield session 414 rather than receiving the key from the external device102.

During the far field session 414, recharge information may be exchangedbetween the IMD 104 being recharged and the external device 102 that isin control of recharging the IMD 104. This recharge information mayinclude diagnostic information that allows the external device 102 tomonitor the recharge efficiency, the status of the battery, and thelike. The external device 102 may control the delivery of the rechargeenergy 416 in response to such diagnostic information such as byincreasing or decreasing the level of recharge energy 416, prompting theuser to adjust the position of the recharge tool, and to eventuallyterminate the recharge session upon detection of a fully rechargedbattery 314. The exchange of recharge information via far fieldtelemetry communications occurs simultaneously with the delivery of therecharge energy as a result of the far field telemetry communicationsbeing significantly out-of-band relative to the recharge energywaveform.

After starting the recharge energy 416, operational flow then carries onwith further interaction between the external device 102 and the IMD104. Examples of these further interactions are set forth in thealternative operations of FIG. 4BA, 4BB, 4BCA-4BCB, or 4BDA-4BDB, whilethe operational flow then concludes in FIG. 4C.

FIG. 4BA shows a first option for operations of the external device 102and the IMD 104. Here, the external device 102 sends a far fieldtelemetry communication 418 that requests the recharge information. TheIMD 104 responds with a far field telemetry communication 420 thatincludes the recharge information. The recharge information may includediagnostic information noted above which may include values such as atally of Coulombs received since a previous request for rechargeinformation which indicates current recharge efficiency as well as animpedance, a voltage, or other value that is representative of thestatus of the battery.

Upon receiving the recharge information, the external device 102 thendetects at a query operation 422 whether the recharge process has anacceptable efficiency based on whether an adequate number of Coulombswere received since the previous request for recharge information. Ifthe charging efficiency is inadequate, then the external device 102 thengenerates an alert to the user at an alert operation 424. The alertindicates to the user that the proximity communicator/recharge head 110needs to be re-positioned closer to the IMD 104. The external device 102then begins repeatedly requesting recharge information at intervalswhile maintaining the far field telemetry communication session in anopen state and maintaining the alert. The external device 102 detectsfrom each response 420 whether the Coulomb count has reached a levelindicative of adequate charging efficiency.

In each of the options shown in FIGS. 4BA, 4BB, 4BCA-4BCB, and4BDA-4BDB, the external device 102 may also monitor the recharge circuit214 to detect changes in the coupling between the coil of the rechargecircuit 214 and the coil of the recharge circuit 312 of the IMD 104.Detecting a change in the coupling of the coils may also indicate thatthere may be a problem with the position. The external device 102 mayutilize the detection of this change together with the Coulomb count toconfirm that the position of the recharge head 110 does need to bechanged. The detection of the change in the coupling may be done at thetime of analyzing the diagnostic information including the Coulomb countreceived from the IMD 104 at the query operation 422. Furthermore, theexternal device 102 may utilize the detected change in the coupling thatmay occur during a suspension period when the far field telemetrycommunication session is temporarily closed to trigger an early end tothe suspension period, which is discussed below in relation to a queryoperation 430. This early end to the suspension period would allow theexternal device 102 to more quickly obtain the diagnostic informationfrom the IMD 104.

Upon the external device 102 detecting that the charging efficiency isadequate, the external device 102 stops generating the alert and thensends an instruction 426 to the IMD 104 to close the communicationsession. The IMD 104 then sends an acknowledgement 428 and deactivatesthe far field telemetry communication circuitry 308. For instance, tothe extent the far field telemetry communication circuitry 308 is astandalone module, the entire module may be powered down. To the extentthe far field telemetry communication circuitry is combined with otherfunctional elements within a common module, the far field telemetrycommunication circuitry 308 portion of the module may be powered down.This begins the suspension period during which time the far fieldtelemetry communications are stopped. To the extent the IMD 104 hasseparate processing for controlling the far field telemetrycommunications, this processing may also be deactivated during thesuspension period to further conserve energy such as by entering a sleepstate or otherwise being powered down as well. Such deactivation relatedto the far field telemetry communications may provide significant energysavings during recharge and thereby reduce the length of the rechargeprocess. It has been observed that in some cases the reduction in thelength of the recharge period due to this deactivation may approach tenpercent or more.

The IMD 104 then begins detecting whether a listen delay period whichsets the interval between attempts to briefly to listen for a wake-upsignal from the external device 102 has ended. When the period of delayhas ended, the IMD 104 then activates the far field telemetrycommunication circuitry 308 to briefly listen for a wake-up signal fromthe external device 102 at a listen operation 436. In this example, theIMD 104 may listen for a few milliseconds. The IMD 104 detects whetherthe wake-up signal has been received at a query operation 438. If awake-up signal has not been received, the IMD 104 deactivates the farfield telemetry communication circuitry 308 and restarts the listendelay period at query operation 434 to delay until the next listenattempt.

Meanwhile, the external device 102 is detecting whether the suspensionperiod noted above for the far field telemetry communication session hasexpired at a query operation 430. The suspension period may be at leastas lengthy as the listen delay period for the IMD 104 and in someembodiments may be significantly longer. For instance, the listen delayperiod may be less than 1 second which ensures the IMD 104 can quicklyenter into far field telemetry communications. The suspension period ofthe external device 102 during a recharge session may be significantlylonger, for instance from 10 seconds to a minute or more, whichsignificantly reduces the amount of energy expended by the IMD 104 incomparison to leaving the far field telemetry communication session openfor the entire recharge session. Thus, lengthening the suspension periodhelps to shorten the time required to complete the recharge process.

Once the suspension period has ended, the external device 102 then sendsa wake-up instruction 432 to open the far field telemetry communicationsession. This instruction 432 is sent at a time when the IMD 104 shouldbe listening at an instance of the listen operation 436. The IMD 104sends an acknowledgement 440 after receiving the wake-up instruction432. If the external device 102 does not receive an acknowledgement 440immediately after sending the wake-up instruction 432, the externaldevice 102 may repeat the wake-up instruction 432 until theacknowledgement 440 is received.

The key being used to encrypt and decrypt the far field messages may beeither a permanent key such as a programming key or a temporary key suchas a recharge key dedicated for one particular recharge session. In thecase of a temporary key, the key may have an expiration. However, wherethe expiration period is computed based on the time from the last farfield telemetry communication, the expiration value of the temporary keyis longer than the suspension period and is therefore still valid ateach point in time when the external device 102 attempts to wake-up theIMD 104 during a given recharge session. Where the expiration period ofa temporary key is computed based on the time from the first far fieldtelemetry communication, the expiration value of the temporary key islonger than the recharge session itself and is therefore still valid ateach point in time when the external device 102 attempts to wake-up theIMD 104 during a given recharge session.

Upon the acknowledgement 440 being received in FIG. 4BA, operationalflow then proceeds to FIG. 4C where the external device sends a request458 for recharge information and the IMD 104 provides a response 460.The external device 102 detects from the recharge information whetherthe battery is fully recharged at a query operation 462. For instance,the external device 102 may detect whether an impedance or voltage ofthe battery 314 has increased to a level indicative of a full charge. Ifthe battery is fully recharged, then the external device stops thetransfer of power for recharge at state 464. Then, the external device102 sends an instruction 466 to close the session for the final time,and the IMD 104 sends an acknowledgement 468 for the final time. If thebattery is not full, then the external device repeats the operations ofFIG. BA, where the request 418 may be sent after closing thecommunication session and delaying for another suspension period.

FIG. 4BB shows a second option for operations of the external device 102and the IMD 104 after the conclusion of the operations of FIG. 4A. Here,the external device 102 sends a far field telemetry communication 418that requests the recharge information. The IMD 104 responds with a farfield telemetry communication 420 that includes the rechargeinformation.

Upon receiving the recharge information, the external device 102 thendetects at a query operation 422 whether the recharge process has anacceptable efficiency based on whether an adequate number of Coulombswere received since the previous request for recharge information. Ifthe charging efficiency is inadequate, then the external device 102 thengenerates an alert to the user at an alert operation 424. The alertindicates to the user that the proximity communicator/recharge head 110needs to be re-positioned closer to the IMD 104. The external device 102then begins repeatedly requesting recharge information at intervalswhile maintaining the far field telemetry communication session in anopen state and maintaining the alert. The external device 102 detectsfrom each response 420 whether the Coulomb count has reached a levelindicative of adequate charging efficiency.

According to some embodiments implementing the option of FIG. 4BB, whilerepeatedly requesting recharge information in order to monitor whetherthe re-positioning of the recharge head 110 is improving the rechargeefficiency, the external device 102 may also be monitoring for aprogramming request from a user at a query operation 442. When aprogramming request is received, the external device may interleave aprogramming instruction 444 with the requests for recharge information,where the IMD 104 responds to the programming instruction 444 with anacknowledgement. Alternatively, the external device 102 may queue theprogramming instruction and then send the programming instruction 444upon determining at the query operation 422 that the recharge efficiencyhas returned to normal levels.

Additionally, upon the external device 102 detecting that the chargingefficiency is adequate, the external device 102 stops generating thealert and then may again detect at the query operation 442 whether aprogramming request has been received from a user of the external device102. If a programming request is received, then the external device 102sends a far field telemetry communication containing the programminginstruction 444. The IMD 104 then responds with the acknowledgement 446.In each of the options discussed herein for FIGS. 4BB through 4BDB thatinvolve sending programming instructions, the far field telemetrycommunication that contains the programming instruction may be encryptedwith a key, such as a permanent programming key or a temporary key suchas the recharge key that is dedicated to the recharge session, that hasbeen previously shared between the external device 102 and the IMD 104,such as by a proximity communication or a low power far field telemetrycommunication.

Additionally, upon the external device 102 detecting that the chargingefficiency is adequate, the external device 102 stops generating thealert and then may again detect at a query operation 442 whether aprogramming request has been received from a user of the external device102. If a programming request is received, then the external device 102sends a far field telemetry communication containing the programminginstruction 444. The IMD 104 responds to the programming instruction 444with the acknowledgement 446.

Operational flow then transitions to FIG. 4C where the operationscontinue as discussed above. If a programming request is not received,then operational flow transitions directly from the query operation 442to the operations of FIG. 4C that continue as discussed above.

FIGS. 4BCA-4BCB show a third option for operations of the externaldevice 102 and the IMD 104 after the conclusion of the operations ofFIG. 4A. Here, the external device 102 sends a far field telemetrycommunication 418 that requests the recharge information. The IMD 104responds with a far field telemetry communication 420 that includes therecharge information.

Upon receiving the recharge information, the external device 102 thendetects at a query operation 422 whether the recharge process has anacceptable efficiency based on whether an adequate number of Coulombswere received since the previous request for recharge information. Ifthe charging efficiency is inadequate, then the external device 102 thengenerates an alert to the user at an alert operation 424. The alertindicates to the user that the proximity communicator/recharge head 110needs to be re-positioned closer to the IMD 104. The external device 102then begins repeatedly requesting recharge information at intervalswhile maintaining the far field telemetry communication session in anopen state and maintaining the alert. The external device 102 detectsfrom each response 420 whether the Coulomb count has reached a levelindicative of adequate charging efficiency.

According to some embodiments implementing the option of FIGS.4BCA-4BCB, while repeatedly requesting recharge information in order tomonitor whether the re-positioning of the recharge head 110 is improvingthe recharge efficiency, the external device 102 may also be monitoringfor a programming request from a user at a query operation 442. When aprogramming request is received, the external device may interleave aprogramming instruction 444 with the requests for recharge information,where the IMD 104 responds to the programming instruction 444 with anacknowledgement. Alternatively, the external device 102 may queue theprogramming instruction and then send the programming instruction 444upon determining at the query operation 422 that the recharge efficiencyhas returned to normal levels.

Additionally, upon the external device 102 detecting that the chargingefficiency is adequate, the external device 102 stops generating thealert and then may again detect at the query operation 442 whether aprogramming request has been received from a user of the external device102. If a programming request is received, then the external device 102sends a far field telemetry communication containing the programminginstruction 444. The IMD 104 then responds with the acknowledgement 446.

Where a programming request has not been received at the query operation442, or where the acknowledgement 446 of a programming instruction 444has been received, the external device 102 then sends an instruction 426to the IMD 104 to close the communication session. The IMD 104 thensends an acknowledgement 428 and deactivates the far field telemetrycommunication circuitry 308 such as by powering down. As noted above, tothe extent the IMD 104 has separate processing for controlling the farfield telemetry communications, this processing may also be deactivatedto further conserve energy such as by entering a sleep state.

The external device 102 then begins detecting whether a programmingrequest has been received from a user at a query operation 448 andwhether the suspension period has ended at a query operation 430.Meanwhile, the IMD 104 begins detecting whether the listen delay periodhas ended at query operation 434. Where a programming request isreceived, then rather than waiting for the end of the suspension period,the external device 102 proceeds to send a wake-up instruction 431 toopen the far field telemetry communication session. This instruction 431is sent at a time when the IMD 104 should be listening at an instance ofthe listen operation 436. The IMD 104 sends an acknowledgement 441 afterreceiving the wake-up instruction 431. If the external device 102 doesnot receive an acknowledgement 441 immediately after sending the wake-upinstruction 431, the external device 102 may repeat the wake-upinstruction 431 until the acknowledgement 441 is received.

Upon receiving the acknowledgement 441, the external device 102 thensends the programming instruction 450. The IMD 104 then sends anacknowledgement 452. The external device 102 then proceeds to send aninstruction 427 to close the far field session. The IMD 104 then sendsan acknowledgement 429.

Upon the suspension period ending at the query operation 430, theexternal device 102 then sends a wake-up instruction 432 to open the farfield telemetry communication session. This instruction 432 is sent at atime when the IMD 104 should be listening at an instance of the listenoperation 436. The IMD 104 sends an acknowledgement 440 after receivingthe wake-up instruction 432. If the external device 102 does not receivean acknowledgement 440 immediately after sending the wake-up instruction432, the external device 102 may repeat the wake-up instruction 432until the acknowledgement 440 is received. Operational flow thenproceeds to FIG. 4C and continues as discussed above.

While the external device 102 is detecting whether a programming requesthas been received at the query operation 448 and whether the suspensionperiod has ended at the query operation 430, the IMD 104 is detectingwhether the listen delay period has ended at the query operation 434.When the period of delay has ended, the IMD 104 then activates the farfield telemetry communication circuitry 308 to briefly listen for awake-up signal from the external device 102 at the listen operation 436.The IMD 104 detects whether the wake-up signal has been received at thequery operation 438. If a wake-up signal has not been received, the IMD104 deactivates the far field telemetry communication circuitry 308 andrestarts the listen delay period at query operation 434 to delay untilthe next listen attempt. Where the wake-up signal has been received, theIMD 104 provides the acknowledgement 440 or 441.

FIGS. 4BDA-4BDB show a fourth option for operations of the externaldevice 102 and the IMD 104 after the conclusion of the operations ofFIG. 4A. In this option, there may be less urgency for sending theprogramming instruction, or the suspension period may be relativelysmall, such as on the order of a few seconds, so that the delay insending the programming instruction is minor. Here, the external device102 sends a far field telemetry communication 418 that requests therecharge information. The IMD 104 responds with a far field telemetrycommunication 420 that includes the recharge information.

Upon receiving the recharge information, the external device 102 thendetects at a query operation 422 whether the recharge process has anacceptable efficiency based on whether an adequate number of Coulombswere received since the previous request for recharge information. Ifthe charging efficiency is inadequate, then the external device 102 thengenerates an alert to the user at an alert operation 424. The alertindicates to the user that the proximity communicator/recharge head 110needs to be re-positioned closer to the IMD 104. The external device 102then begins repeatedly requesting recharge information at intervalswhile maintaining the far field telemetry communication session in anopen state and maintaining the alert. The external device 102 detectsfrom each response 420 whether the Coulomb count has reached a levelindicative of adequate charging efficiency.

According to some embodiments implementing the option of FIGS.4BDA-4BDB, while repeatedly requesting recharge information in order tomonitor whether the re-positioning of the recharge head 110 is improvingthe recharge efficiency, the external device 102 may also be monitoringfor a programming request from a user at a query operation 442. When aprogramming request is received, the external device 102 may interleavea programming instruction 444 with the requests for rechargeinformation, where the IMD 104 responds to the programming instruction444 with an acknowledgement. Alternatively, the external device 102 mayqueue the programming instruction and then send the programminginstruction 444 upon determining at the query operation 422 that therecharge efficiency has returned to normal levels.

Additionally, upon the external device 102 detecting that the chargingefficiency is adequate, the external device 102 stops generating thealert and then may again detect at the query operation 442 whether aprogramming request has been received from a user of the external device102. If a programming request is received, then the external device 102sends a far field telemetry communication containing the programminginstruction 444. The IMD 104 then responds with the acknowledgement 446.

Where a programming request has not been received at the query operation442, or where the acknowledgement 446 of a programming instruction 444has been received, the external device 102 then sends an instruction 426to the IMD 104 to close the communication session. The IMD 104 thensends an acknowledgement 428 and deactivates the far field telemetrycommunication circuitry 308. As noted above, to the extent the IMD 104has separate processing for controlling the far field telemetrycommunications, this processing may also be deactivated to furtherconserve energy.

The external device 102 then begins detecting whether a programmingrequest has been received from a user at a query operation 448 andwhether the suspension period has ended at a query operation 433.Meanwhile, the IMD 104 begins detecting whether the listen delay periodhas ended at query operation 434. Where a programming request isreceived, then rather than proceeding to send a wake-up instruction toopen the far field telemetry communication session, the external device102 waits for the end of the suspension period as detected at the queryoperation 433.

Upon reaching the end of the suspension period, the external devicesends a wake-up instruction 432. This instruction 432 is sent at a timewhen the IMD 104 should be listening at an instance of the listenoperation 436. The IMD 104 sends an acknowledgement 440 after receivingthe wake-up instruction 432. If the external device 102 does not receivean acknowledgement 440 immediately after sending the wake-up instruction432, the external device 102 may repeat the wake-up instruction 432until the acknowledgement 440 is received.

Upon receiving the acknowledgement 440, the external device 102 thensends the programming instruction 450. The IMD 104 then sends anacknowledgement 452. The external device 102 then proceeds to send aninstruction 454 to close the far field session. The IMD 104 then sendsan acknowledgement 456. The external device 102 then continues to detectwhether a programming request has been received at the query operation448 and whether the suspension period has ended at the query operation433.

Where a programming request is not received by the time the end of thesuspension period is reached, the external device sends a wake-upinstruction 432. This instruction 432 is sent at a time when the IMD 104should be listening at an instance of the listen operation 436. The IMD104 sends an acknowledgement 440 after receiving the wake-up instruction432. Operational flow then proceeds to FIG. 4C and continues asdiscussed above.

While the external device 102 is detecting whether a programming requesthas been received at the query operation 448 and whether the suspensionperiod has ended at the query operation 433, the IMD 104 is detectingwhether the listen delay period has ended at the query operation 434.When the period of delay has ended, the IMD 104 then activates the farfield telemetry communication circuitry 308 to briefly listen for awake-up signal from the external device 102 at the listen operation 436.The IMD 104 detects whether the wake-up signal has been received at thequery operation 438. If a wake-up signal has not been received, the IMD104 deactivates the far field telemetry communication circuitry 308 andrestarts the listen delay period at query operation 434 to delay untilthe next listen attempt. Where the wake-up signal has been received, theIMD 104 provides the acknowledgement 440 or 441.

While embodiments have been particularly shown and described, it will beunderstood by those skilled in the art that various other changes in theform and details may be made therein without departing from the spiritand scope of the invention.

1. A method of recharging an implantable medical device, comprising:establishing a far field telemetry communication session with theimplantable medical device; transferring power over a proximity couplingto the implantable medical device during the far field telemetrycommunication session; receiving recharge information from theimplantable medical device via the far field telemetry communicationsession while transferring power to the implantable medical device; andafter receiving the recharge information, suspending the far fieldtelemetry communication session for a period of time while transferringpower to the implantable medical device. 2-30. (canceled)